Run clang-tidy modernize-use-equals-{delete,default} on //net/proxy/proxy_resolver_v8_tracing.cc

See the bugs and cxx post for justification and details:
https://groups.google.com/a/chromium.org/forum/#!topic/cxx/RkOHzIK6Tq8

This change was done using clang-tidy as described here:
https://chromium.googlesource.com/chromium/src/+/lkcr/docs/clang_tidy.md

In some cases the the tool leaves behind a string of commas where it
replaced a member initializer list
(https://bugs.llvm.org/show_bug.cgi?id=35051). They were cleaned up with:
  git diff --name-only | \
    xargs sed -E -i 's/(^\s*|\)\s*):[ ,]*= default/\1 = default/'

BUG=778959,778957
This CL was uploaded by git cl split.

R=jochen@chromium.org

Change-Id: Ie446e2916697e7878d30abe052018508897b2dc7
Reviewed-on: https://chromium-review.googlesource.com/799513Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Commit-Queue: Chris Watkins <watk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520791}

net/proxy/proxy_resolver_v8_tracing.cc

@@ -1081,8 +1081,8 @@ class ProxyResolverV8TracingFactoryImpl::CreateJob
   DISALLOW_COPY_AND_ASSIGN(CreateJob);
 };
 
-ProxyResolverV8TracingFactoryImpl::ProxyResolverV8TracingFactoryImpl() {
-}
+ProxyResolverV8TracingFactoryImpl::ProxyResolverV8TracingFactoryImpl() =
+    default;
 
 ProxyResolverV8TracingFactoryImpl::~ProxyResolverV8TracingFactoryImpl() {
   for (auto* job : jobs_) {